TSB 18-06-98

Hard starting diagnosis.

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Models: 94-98 12 valve Cummins up to 01/01/98

NOTE:   THIS INFORMATION APPLIES TO ALL 5.9L CUMMINS MECHANICALLY INJECTED 12 VALVE DIESELS USED IN THE RAM.

Symptoms: hard or no-start

Diagnosis:

Using  table of values to refer to for timing and other information, determine the cause of the problem. Hard start or no start complaints can be caused by several problems - the following points have a short discussion of the main problem:

1.   low fuel pressure or air entering the system:

• This can cause low rpm miss/instability, white smoke, hard starting, or low power.  Basic fuel system diagnostics should be followed.  TSB 14-07-96 should be referenced when diagnosing fuel concerns.

• A leak in the fuel return portion of the fuel system can allow air to enter the injection pump eventually. An area to inspect is the 5/16" rubber hose that connects to a steel line on the back of the injection pump. Replace the line if it is leaking or leaking is suspected.  NOTE, this line, located behind the fuel filter, has failed on my truck, and several others.

• In ambient temperatures below 60 F (15 C), the throttle should be partially depressed after engaging the starter.  If the engine will not start, full throttle should be applied.  Hard starting in temperatures above 60 F (15 C) can be produced by too low an idle speed.  Lower idle speeds increase the need to depress the throttle to start the engine.

• Late injector pump timing affects starting and excessive white smoke in ambient temperatures below 20 F (-6 C).  See chart for a list of injection pump timing specs.

• The intake manifold heater grid affects starting in sever cold weather.  Verify proper preheat cycling of the grids by following diagnostic procedures listed in service and diagnostic manuals.

• Number 2 diesel fuel can gell at temperatures below 20 F (-6 C). For hard/no start conditions in extreme cold temperatures, inspect for waxing in the fuel filter element.  If waxing is found, diagnose for fuel heater operation in the appropriate service and diagnostic manuals.

*The injection pump for 94 and early 95 model year trucks p/n R4761366 was superseded to R4798548. If the vehicle has the new p/n R4798548, the engine data tag should have been stamped as CPL 1968 and timing spec for CPL 1968 should be used for the superseded pump.

Policy: Information only.

This page was edited on: May 3, 2004